Glossary — M
15 terms
Mission
A planned spaceflight objective with defined goals, vehicles, and phases.
Example: The science mission mapped the Moon's gravity field.
MEO
Medium Earth Orbit: an orbit between roughly 2,000 km and 35,786 km altitude, most notably used by navigation constellations.
Example: GPS satellites fly in medium Earth orbit at about 20,200 km.
Max-Q
The point of greatest aerodynamic stress during ascent or entry.
Example: The vehicle throttled down to ease loads through Max-Q.
Magnetorquer
A coil that pushes against Earth's magnetic field to dump momentum.
Example: Magnetorquers desaturate reaction wheels in low Earth orbit.
Monopropellant
A single propellant that decomposes or burns without a separate oxidizer.
Example: Hydrazine is a common monopropellant for small thrusters.
Multi-layer insulation
Layered reflective blankets that insulate a spacecraft from thermal extremes.
Example: Gold-colored multi-layer insulation blankets the spacecraft exterior.
MECO
Main Engine Cutoff: the shutdown of a stage's main engine at the end of its burn.
Example: MECO was confirmed, and the stage separated cleanly.
Mach number
The ratio of a vehicle's speed to the local speed of sound.
Example: The vehicle was supersonic, above Mach 1, soon after liftoff.
Meteorology mission
A mission focused on weather monitoring and forecasting.
Example: Geostationary meteorology missions watch storm development.
Momentum dump
Periodically offloading reaction-wheel momentum using thrusters or torquers.
Example: Momentum dump fired thrusters to reset the wheels.
Mars mission
A mission whose destination is Mars.
Example: The Mars mission searched for signs of ancient water.
Molniya orbit
A highly elliptical, high-inclination orbit with apogee over high northern latitudes.
Example: Russia uses Molniya orbits to cover its far-north regions.
Mesosphere
The layer above the stratosphere where most meteors burn up.
Example: Meteors ablate in the mesosphere.
Mass flow rate
The amount of propellant consumed per unit time.
Example: Higher mass flow rate increases thrust for a given exhaust velocity.
Multi-year mission
A mission designed to operate for many years.
Example: The multi-year mission returned data for over a decade.